1. Field of the Invention
This invention relates to a thermally conductive composition layer of high thermal conductivity, thermally conductive particles and a thermally conductive composition that can be used in forming such a layer, an electronic device having that thermally conductive composition layer between layers thereof, and a method of forming the thermally conductive composition layer. The present invention relates mainly to cases where adhesiveness is required.
More particularly, the present invention relates to a thermally conductive composition layer exhibiting high thermal conductivity and to raw material therefor, used in cases where such are employed as an adhesive layer between heat generating bodies such as electronic components including semiconductor devices as well as mounting boards and heat radiating bodies or other components, to electronic components for which such are employed, and to a formation method therefor.
Because it is an invention wherewith such thermal conductivity can be achieved by the presence of a metal or alloy, the fact that outstanding thermal conductivity is exhibited can also mean that electrical conductivity is excellent in the present invention. Accordingly, the present invention relates also to an electrically conductive composition layer of high electrical conductivity, electrically conductive particles and an electrically conductive composition that can be used in forming such a layer, an electronic device having that electrically conductive composition layer between layers thereof, and a method of forming the electrically conductive composition layer.
In other words, in the specification of this application, the term “conductivity” comprehends both “thermal conductivity” and “electrical conductivity.”
2. Description of the Related Art
In electronic devices such as semiconductor devices of recent years, advances are being made in achieving increasingly high-density mounting and higher integration, and ever higher speeds are being sought.
In conjunction with this trend, the amount of heat generated when driving electronic components is tending to increase, and there is a danger of causing electronic component performance to decline unless cooling is done efficiently.
One method that is used for cooling electronic components is a method of joining heat sinks and the like by die bonding to semiconductor devices or to circuit boards whereon such electronic components are mounted. When that is done, in order to improve cooling efficiency, improving the performance of the heat sink is of course necessary, but it is also necessary to enhance the thermal conductivity of the bonding materials used in joining the electronic components and the heat sink or other cooling components.
For that reason, techniques are adopted for improving cooling efficiency by using bonding materials of high thermal conductivity between a heat sink and an electronic component or the like. More specifically, thermal conductivity is imparted by mixing a filler powder of high thermal conductivity suitably into an epoxy resin, silicone resin, or the like, so that cooling efficiency is improved by using that material to bond the heat sink or the like to an electronic component such as an LSI device.
Furthermore, since, in an LSI device package such as a CSP, copper or some other heat spreader is joined by die bonding to the LSI device by means of an adhesive such as a silicone resin, materials of high thermal conductivity are also wanted for the bonding material.
To date, for such materials, inorganic metal compounds of high thermal conductivity, such, for example, as aluminum oxide (Al2O3), aluminum nitride (AlN) powder, and silica (SiO2) powder, are mixed into an epoxy resin or silicone resin and used.
At such time, moreover, for the filler powder and the resin material mixed together, highly insulative materials have been used for the purpose of preventing electronic component from short-circuiting.
However, there is a limitation in dramatically improving thermal conductivity by simply applying this type of mounting configurations wherein an inorganic filler is mixed. Furthermore, in order to improve cooling efficiency, it is necessary to use materials of high purity or the like, leading to problems of increased material costs.
Meanwhile, one of the main reasons for the necessity of using highly insulative materials as noted above, is as follows. When bonding is being effected, a bonding material that spreads out from the bonding area makes contact with other components, causing electronic components to be short-circuited. Thus, if only there were no such spreading out, it would often be possible to employ metallic bonding at the bonding site, whereupon one could expect a sharp improvement in cooling efficiency due to the sharp enhancement of the coefficient of thermal conductivity.
Such art is seen in Japanese Unexamined Patent Application Publication No. H8-227613/1996, wherein it is proposed that, by effecting heat treatment of a composition comprising material wherein a copper powder is coated with tin or similar metal, and a thermosetting polymer having a high curing temperature such as polyimide, the coating metal is melted, and mutual bonding thereof is effected.
In this invention, however, only a high-temperature process is disclosed as a specific process, where, for example, it is necessary to realize a temperature as high as the melting point (about 231° C.) or above of tin in order to melt tin used as a coating metal, while it is also necessary to effect heat treatment at 300 to 400° C. in order to cure the thermosetting resin. Accordingly, it is difficult therewith to avoid the problem of thermal damage to substrates, LSI's, and materials peripheral thereto.
Similar art is disclosed in Japanese Unexamined Patent Application Publication No. H10-265748/1998, wherein the art disclosed is for heat treating at 230° C.
In that invention also, however, it is necessary to heat to a temperature as high as the melting point or above of a coating metal in order to melt the coating metal, and there is little freedom to select a heat treatment temperature.